1. Field of the Invention
The present invention relates to a belt adjusting device for an endless belt set among a plurality of rolls, which device is configured so as to automatically correct the movement in the cross direction of the belt or the zigzag or meandering movement of the endless by correcting lengthwise shifts in the running direction of each side edge of the endless belt.
The present invention also relates to a single facer having a belt adjusting device which is configured so as to correct a zigzag or meandering movement of an endless belt in the cross direction and/or shearing deformation of the endless belt and resulting contraction of the belt width occurring as the endless belt runs applying bonding pressure on paper webs being processed.
2. Description of the Related Art
Conventionally, when manufacturing an endless belt which runs around a plurality of rolls in sequence into an endless form, it is very difficult to make the lengths of belt edges on opposite sides to be exactly the same dimension with high accuracy. Moreover, elongation of the belt occurs variably at right and left side edges over extended periods of use, or various factors such as slight inaccuracy of parallelism among the rolls at the time of manufacture may cause relative shifts between the two side edges of the belt. As a result, the endless belt 3 may move toward one side in the roll axis direction or tend to move in a zigzagging manner. With relative differences in the amount of running motion (lengthwise shifts) of the side edges of the belt, shrinkage of the belt width W in the cross direction may arise. This tendency of shrinkage is more expressed when the slip of the belt with respect to the rolls is less or, in other words, when the tension of the belt is higher.
A conventional method for correcting such tendency in dynamic belt motion has been to visually check the condition of the belt and then change the angle of the rotating shaft of some rolls to manually adjust the tension at each side edge of the belt.
With this conventional method, however, human attention is required frequently, and a high level of technical skill is needed in correcting the shift caused by various factors. Under these circumstances, some measures have been desired for easily correcting shifts in belt position at each side edge of the belt without human intervention.
On a single facer, corrugation is formed on a medium between a rotating corrugating roll 54 and another corrugating roll 54' engaging with each other, as shown in FIG. 17. Paste is applied to the top portions of corrugation on the corrugated medium, and a liner is bonded to the medium by pressing the liner against the medium by means of an endless belt 53 to produce a one-side corrugated fiberboard which has a flat surface on one side and a corrugated surface on the other side. The endless belt 53 is driven by at least a pair of parallel belt rolls 51 and 52.
FIG. 18 is a view for illustrating the occurrence of zigzag or sideway movement while a power-transmitting endless belt is running and a device for adjusting the zigzag movement. As described above, it is difficult to manufacture the endless belt 53, which runs around a plurality of belt rolls 51 and 52, so as to make the lengths of opposite side edges thereof to be exactly the same. Also, as the endless belt 53 is used over extended periods of time, two side edges of the belt become elongated differently or poor parallelism of the rolls 51 and 52 causes the endless belt 53 to shift in the cross direction (i.e., the direction along the roll axis) or move in a zigzagging manner while the endless belt 53 is running. As a result, not only the belt 53 collides with a housing 59, but also the manufacture of single-sided corrugated fiberboard at the edge portion cannot be done because the position of the belt 53 shifts beyond the width of the product.
To solve these problems, for endless belts in general, after the conditions of zigzag or sideway movement and shift are checked by eyes or by a detector, an adjustment is made by manually changing the tension of each side edge of the belt. This adjustment, which is made by an operator, is done by changing the direction of the rotating shaft of the roll 52 by means of a cylinder 56a or 56b in the plane in which the belt runs.
When such an adjusting method alone is applied to a single facer, however, deviations in relative movement between opposite side edges tend to occur easily because the belt is very wide relative to its length, unlike common endless belts. As a result, the belt width W decreases, or the life of the belt is shortened due to shear deformation in the plane of the belt. Also, for such a wide belt, the position of the belt on the roll tends to shift in the cross direction because there normally exist some differences in belt length between the side edge portions even if no relative differences in belt tension exist between the opposite side edge portions of the belt.
Therefore, on the single facer, in addition to the device for adjusting the tension of the side edge portion, a different type of devices have been desired for belt adjustment to solve the above-described problems inherent in the single facer.